This invention relates to a wireless telephone system for employing one or a plurality of orbiting satellites to allow wireless telephone users (subscribers) communication access to a terrestrial telephone system (whether private, government or common carrier), and particularly to a wireless telephone system, such as a cellular system, which permits subscriber access to terrestrial telephone networks while the subscriber is roaming in areas that do not have cellular telephone services.
There is a need to provide personal communications anywhere on the earth. Current communications systems, for example, cellular telephone systems, require terrestrial cellular relay stations to intercept and link a cellular radiotelephone transmission with conventional switched telephone users and with other cellular telephone users.
Cellular telephone systems have been proposed which account for roamers, i.e., cellular telephone users which roam outside a normal service area. The American Telephone and Telegraph Corp. (AT&T) has proposed an inter-cellular data network for interconnecting terrestrial cellular telephone service areas using a terrestrial packet-switched network that has nodes at the participating cellular telephone service areas wherein packet-switched network data is accumulated in a database of roaming cellular telephone users. The database therein proposed would keep track of roamers and allow terrestrial interconnection of the roamer to the telephone system when the roamer is located in a cellular telephone service area that is remote from a designated home cell. Certain data is collected which would allow routing of calls to the roaming user, allow issuance of billing information, and allow collection of other system operation data. The operation of the system is proposed as follows: A database of roaming users is notified via the user when the user desires to accept or make telephone calls while roaming. The user notifies the system of intention to roam via a digital signal from the cellular telephone. The roaming user is then logged into the database via a terrestrial or other packet-switched network. Upon entering a participating remote cellular telephone service area, the mobile transceiver apparatus would transmit a (burst) digital signal to the cellular telephone operator in the remote service area. The database of roaming users would then be updated to show the user's current service area. Incoming calls normally directed to the user home cell are thus routed to the proper service and switched to the user. Call screening and other features would allow the user to control the expenses. For outgoing calls, connections are made from the mobile transceiver apparatus to the current service area, which in turn handles connections to the public switched telephone system in the normal manner of cellular telephones. Means may be provided to provide for billing of the user via his home cell due to the database information provided by the packet switched data network.
Efforts are under way to utilize satellite technology in cellular communications. Satellite delivered telephone services to mobile users has been proposed as the Mobile Satellite System (MSS) in the USA. This system is now being implemented by the American Mobile Satellite Corp. (AMSC). It utilizes transceivers in the mobile unit (automobile for example) operating in the L-band (1530-1560 MHz and 1646.5-1660.5 MHz) that communicate to a satellite at geosynchronous orbit. In addition to significant expense to the end user for the transceiver apparatus, the system is subject to noticeable relay delay due to transmission of the signals to and from geosynchronous orbit. Furthermore, the cellular telephone service providers must nevertheless implement a costly additional inter-system network to direct calls to the mobile transceiver apparatus. The current system as envisaged does not have a method for locating the roaming user and directing the call to the user.
A search of U.S. Patent office records uncovered U.S. Pat. No. 4,972,456, assigned to GTE MobileNet, which discloses a cellular telephone "satellite" roaming system that uses a satellite system to permit access to the cellular telephone system when a user is located in areas outside of cellular telephone system coverage This system does not contemplate overhead orbiting satellites, but rather the system would employ subsidiary cell sites in a terrestrial-based cellular communications system.
Other patents uncovered relate to general information on cellular telephone roaming systems which permit a user of one cellular system to use another cellular system while traveling in areas outside a home cellular system. These patents include U.S. Pat. Nos. 4,901,340; 4,972,460; and 4,833,701.
Motorola, Inc. announced on Jun. 27, 1990 a proposed crosslinked satellite network under the name IRIDIUM. The IRIDIUM system is believed to be described in European Patent Publication EP 365,885, published May 2, 1990, and corresponding to U.S. patent application Ser. No. 263,849 filed 28 Oct. 1988 now abandoned. The IRIDIUM system envisions a rigid constellation of seventy-seven low-earth orbiting satellites in seven circular polar orbits for supporting cellular telephone communications on the earth's surface. In the IRIDIUM system, all handoff and relays of communications traffic are handled in space directly between satellites, so that the terrestrial telephone network is bypassed. However, ground signal processing is required to set up and place calls. Calls originating from outside the satellite service areas must interrogate the home location of the user in order to identify the user. The system requires that all satellites be linked constantly to one another. Each of eleven evenly-spaced satellites sharing an orbit is contemplated to project thirty-seven communications cells on the earth's surface. Due to cost and channel limitation, it may be presumed that the IRIDIUM system will not compete with the services provided by terrestrial-based cellular communications systems. A technical description of this invention is believed to be contained under U.S. patent application Ser. No. 263,849 filed Oct. 28, 1988 in the names of Bertiger, Leopold and Peterson.
By a document dated Nov. 2, 1990, Ellipsat Corporation made application to the Federal Communications Commission for authority to construct an elliptical orbit satellite system to support, among other things, mobile voice services in the United States through a constellation of six satellites. The service has been presented as complementary of and not competitive with existing and future (terrestrial) cellular telephone services. The system contemplates the use by end users of dual-mode transceivers using Carrier Division Multiple Access (CDMA) modulation to effect communications with earth satellites in extended-coverage elliptical orbit.
Current technology in the cellular telephone industry uses analog transmission at 30 kHz FM with many customer features such as autodial, portable operation etc. The next generation of equipment will be Time Division Multiple Access (TDMA) digital transceivers, due to be introduced in late 1990. Future generations of Cellular Telephones will use Code Division Multiple Access (CDMA) and spread spectrum modulation for solutions to communication traffic saturation of terrestrial cellular systems. Finally, a roaming network is being developed for the purpose of allowing cellular telephone customers the ability to roam from cell system to cell system in the USA (and other regions).
In the development of commercial terrestrial-based cellular telephone systems, it is expected that dual mode radios will be produced that will be able to access both analog and digital systems. With digital radios, additional services are expected to appear such as car to mobile facsimile (car fax), data transmission, computer interconnections and position location services.
Some high usage cellular systems, such as PACTEL's Los Angeles system, are expected to saturate in 1991. PACTEL and other cellular systems are looking toward Time Division Multiple Access (TDMA) as a step toward satisfying future needs. However, the system operators see even more capacity demands and have funded development of a CDMA-based technology. QUALCOMM in San Diego, California, has been funded by NYNEX and others to develop CDMA technology for cellular services. QUALCOMM has demonstrated a 9.6 KBPS voice codec with "toll quality" performance using CDMA technology. CDMA may become an industry standard since it is expected to relieve the "capacity" problem and is inherently less expensive as cell site equipment, particularly for rural service areas (RSAs).
CDMA may be used in connection with implementations of the present invention, but the use of other modulation schemes is not precluded.